Stilbene from benzyl mercaptan



Patented July 14, 1953 2,645,671 STILBENE FROM BENZYL MERCAPTAN Leonard A. Mattano, Hammond, Ind., assignor'to Standard Oil Company, Chicago, 111., a corporation of Indiana 'NoDrawing. Application June 20,1951, Serial No. 232,663

I have found that stilbene and its derivatives 7.

can be obtained by heating, to at least 150C. and

preierably to standard boiling temperature or above, a'benzyl mercaptan having theformula in which R can be hydrogen,.or an alkylorlalkoxy group, in the presence of .a sulfactive catalyst comprising one or more of the sul'fides,po1ysu1- fides or oxides. of themetals molybdenum, cobalt, iron, silver, copper, .manganese,.niCkeLaridlead.

Thecatalyst can be brought intocontact with-the mercaptan as a salt or oxideof .themetaLin-Which case it will be converted to the sulfide .in. the reaction zone. .Sulfactive catalystsrare described in Lazier et al., U. S. 2,221,804.

Benzyl mercaptans can be .made .fromlbenzyl chloride or ring-substituted benzylchlorides by sulphydrolysis (.Loverde U. S. 2,456,588) .or'from benzaldehyde, hydrogen and sulfur, reactedin the presence of iron sulfide (Far-low et al., I]. S. 2,402,615).

Hydrogen sulfide is Jiberated during the course of .reaction and is expelled from the synthesis system. Themercaptanreactantvapors liberated from the boiling reaction mass'are'condensed'and the condensate is refluxed to the reaction zone. Preferably, an inert 'gas ispassed through the reaction massand is employed'to strip'reaction product and carry it therefrom "to a condensing zone. Suitable stripping gases 'arenitrogen, carbon dioxide and ammonia. The liberated hydrogen sulfide will also aid in stripping the reaction product. 7

When the reaction 'isfcarried out at atmospheric pressure the initialreaction temperature will usually be the refiuxingtemperature, between about 190 and 200 C of benzyl'mercaptan at this pressure. An inert gas is used to strip lighter boiling ,by-products,' such as Ltoluene, ifrom the reaction :mixture. .during .the reaction. ".The refluxing temperature will increase during the course of reaction andp atatmospheric r pressure,

will approach the boiling'temperaturezof stilbene, or about 300 C. The refluxing .eanhbeicarried out at low pressures and temperatures; an. initial temperature of at least about C. will be ada quate to initiate the synthesis. Temperatures considerably in excess of'300 C. iorexample, temperatures above 325 C., will'causethe process to encounter side reactions resulting in undesirable decomposition of the benzyl mercaptan. When the preparation is carried out under "atmospheric pressure, a reaction period from about one-half to three hours is preferred. Higher pressures and resultant higher reflux temperature require shorter reaction times.

The reaction product can be condensed directly to solid form .in, :for example, such condenser chambers as are-employed-insthe manufacture of phthalic anhydride. The 'stilbene or derivative material can be Washed'with water ormost hydrocarbon solvents or it can be dissolvedin concentrated or 1 absolute alcohol rand be recrystallized therefrom. The recrystallizedmroductwhen unsubstituted benzyl mercaptan isremployedas feed stock Will be transestilbene, which has a melting point of 12412 C. and a boiling point of 306.5" C.

The catalyst can either be dispersed in finely dividedform in the boiling reactant or it can be deposited upon supportin wmaterial .such as kieselguhr, alumina; carbon or clay. A column packedwith catalyst, preferably supported catalyst, can be employed and .thebenzylmercaptan can either trickle over the catalystor bepassed through the column :as a vapor. The relative quantity of catalyst is not critical, butpreferred operating conditions require .a relative -,quantity o'f catalyst dispersed in boiling liquid of .at'least about 0.5 part by weight of catalyst based on the 'weight of the reactant. Thecatalyst canalso be dispersed in a fluidized, dense phase through which. vaporized benzyl mercaptan ispassed. If a packed column or a fluidized catalystphaseis employed, space velocities between about .0.1.an.d 10 are preferred,

When benzyl .mercaptan is, passed ,as. ayapor through apacked column, the-preferred temperature and pressureshould be such thatthe-stilbene which is formed will also .be -.in vapor form. Efiiuent vapors .from :the packed tower .can be passed .to a condensingzoneiand (200186."130932136111- .perature below about 300 C. .and above about 200 C. for recovery of stilbene. flfaporsfiowing from the stilbenerecovery zone can be condensed and the condensate can be recycled to equipment for vaporizingthe benzy-l mercaptan.

The following specific examples, which are supplied for the purpose of illustrating the invention, demonstrate preparation of stilbene in the presence of various catalysts.

EXAlWPLE I A vessel equipped with stirring apparatus was charged with 106 parts by weight of benzyl mercaptan and parts by weight of molybdenum disulflde. condenser and apparatus for the introduction and dispersion of inert gas within the reaction zone. The reaction mixture, while being stirred, was heated at atmospheric pressure to the boiling point which, initially, was 194 C. Ammonia was bubbled through the solution throughout the course of the reaction. Boiling of the reaction mixture and refluxing of condensate was continued for a period of about two hours, during which time the reflux temperature rose to about 300 C. About one-half of the total volume of benzyl mercaptan was stripped along with the reaction product and was carried in the ammonia stream through the condenser. In commercial operation this mercaptan can be condensed and returned to the reaction zone. Solid reaction product consisting of 9 parts by weight of stilbene was recovered from the condenser; this constituted a yield of about 24.5 percent based on the converted benzyl mercaptan. Hydrogen sulfide was continually evolved during the reaction, which can be represented by the following equation:

An analysis of the reaction product and the reportedvalues for trans-stilbene are shown in the table below:

Apparatus similar to that described in Example I was charged with 58 parts by weight of benzyl mercaptan and 5.0 parts by weight of copper sulfide. The benzyl mercaptan was refluxed at atmospheric pressure and at an initial temperature of 194 C. The boiling temperature gradually rose to 300 C. The mixture was stirred, nitrogen was passed slowly through the mixture and hydrogen sulfide was continuously evolved during the reaction period. The reaction product was separated as a solid from the eiiiuent vapors. The solid condensate was dissolved in hot alcohol and filtered. Stilbene was crystallized from the filtrate and was obtained in an approximately percent yield. The product had a melting-point range of 116 to 120 C. compared to a melting point of 124 C. reported in the literature for stilbene.

EXAMPLE III Benzyl mercaptan was refluxed, in the equip- The vessel was fitted with a reflux ment and according to the process described in Examples I and II, and in the presence of slightly over 10 percent by weight, based on the mercaptan, of cupric oxide catalyst. Nitrogen was passed through the reaction mixture and hydrogen sulfide was evolved therefrom throughout the course of the reaction. A yield of about 20 percent by weight of stilbene was obtained as condensate of the effiuent vapors from the boiling mercaptan. The obtained stilbene melted in the range of 117 to 121 C.

EXAMPLE IV EXAMPLE V Benzyl mercaptan. was heated at an initial rcflux temperature of about 194 C. and to a final reflux temperature of about 300 C. in the presence of about 10 percentby weight, based on the mercaptan charged, of a catalyst consisting of molybdenum oxide deposited on bauxite. Nitrogen was passed through the reaction mixture and hydrogen sulfide was evolved therefrom throughout the course of the reaction. stilbene was obtained in a yield of approximately 20 percent.

EXAMPLE VI Benzyl mercaptan was heated for a period of about one hour from an initial reflux tempera ture of 194 C. to a final temperature of about 280 C. in the presence of about 10 per ent by weight, based on the mercaptan charged, of a catalyst consisting of nickeloxide deposited on kieselguhr. Nitrogen was passed slowly through the stirred reaction mixture and hydrogen sulfide was continually evolved during the course of the reaction. Stilbene vapors carried by the sweep gases were deposited in the condensing apparatus as a solid. The solid was recrystallized 7 from alcohol and dried. The stilbene product,

which was obtained in a yield of about 20 percent by weight, melted in the range of to 122 C.

EXAMPLE VII EXAMPLE VIII Benzyl mercaptan was refluxed for a period of about two hours from an initial temperature of about C. to a final temperature of about 300 C. in the presence of a catalytic amount of anner-1 Was removed therefrom. .Stilbene was; condensed in the condensing zone. I hestilbene product,

which was recrystallized pom ethyl alcohol, melted'in the range of 116-124 C.

' EXAMPLEIX Seventy-five grams of paramethoxybenzylmer captan wererefluxed'from' an initial temperature of about 175 C. to a"flnailtemperature-ofabout 300 C. in the presence of about 7 percent by weight of finely divided molybdenum disulflde. Nitrogen was passed through the reaction mixture, and hydrogen sulfide was removed therefrom throughout the reaction period. The product was washed with hot ethyl alcohol to remove color bodies and then recrystallized from hot benzene. Pearl-white crystals having a melting point range of 213.5 C.215 C. were obtained. The reported melting point ranges for 4,4 dimethoxy stilbene are 213-214 C. and 214-215 C.

Various method can be employed in carrying out the present process. For example, rapid reaction can be obtained by placing the benzyl mercaptan and catalyst mixture under pressure so that boiling and reflux of the benzyl mercaptan will begin at an initial'high temperature. In a preferred embodiment of this procedure the temperature can be maintained at a uniform level throughout the reaction by adjusting the pressure at the beginning so that the initial boiling temperature will be substantially the temperature of boiling stilbene at atmospheric pressure. As the reaction progresses and the concentration of stilbene in the reaction zone increases the pressure can be continually reduced to prevent increase in boiling temperature. manner any temperature above about 150 C. and below about 325 C. can be maintained throughout the reaction period. Although the foregoing examples describe a process wherein the produced stilbene is vaporized from the reaction mass during the reaction period, and although the employment of the sweep gas to remove stilbene from the reaction Zone is preferred, synthesis of stilbene can be accomplished by carrying out the reaction under conditions whereby hydrogen sulfide is continually removed from the reaction zone while stilbene remains.

As hereinbefore mentioned, the product stilbene is condensed as a solid from the vapors flowing from the boiling reaction mixture. lhe stilbene can be condensed in large cooling chambers or it can be scrubbed from the reaction product gases with concentrated or absolute alcohol, from which the stilbene will then be crystallized.

Stilbene and its derivatives are primarily useful in the manufacture of dyestufls and to a minor extent as pharmaceuticals and organic intermediates.

Having described my invention, I claim:

1. A process of making stilbene and stilbene derivatives comprising the steps of heating a benzyl mercaptan, having the structure:

in which R is selected from the group consisting of hydrogen, alkyl and alkoxy radicals, at a tem- 6 -'perature-at-least abov about 150' C. in the presence of 'a' s'u'lfactive catalyst ,3 and: separating. a stilbene pro'duct. from? the reaction mass.

c1112. Amrocesstofimaking' stilbene comprising the stepsaof: heating a benzylzrmercaptan, having the structure: Y

in which R is selected from the group consisting of hydrogen, alkyl and alkoxy radicals, at a temperature at least above about 150 C. in the presence of a sulfactive catalyst comprising essentially a compound of a metal selected from the group consisting of iron, cobalt, nickel, copper, silver, lead, manganese, and molybdenum and separating a stilbene product from the reaction mass.

3. A process of making stilbene comprising the steps of heating benzyl mercaptan to a, reflux In a similar 7 temperature under a pressure such that the initial reflux temperature is at least above C. in the presence of a sulfactive catalyst comprising essentially a compound of a metal selected from the group consisting of iron, cobalt, nickel, copper, silver, lead, manganese, and molybdenum, refluxing the said mercaptan in the presence of the catalyst and effecting decomposition and condensation of the said mercaptan while evolving hydrogen. sulfide and product vapors, and condensing stilbene from the effluent product vapors.

4. A process of making stilbene comprising the steps of heating benzyl mercaptan to a temperature between about 150 and 325 C. and at least at atmospheric pressure in the presence of 0.5 to 20 percent by weight of a sulfactive catalyst comprising essentially the sulfides of a metal selected from the group consisting of iron, cobalt, nickel, copper, silver, lead, manganese and molybdenum, refluxing the said mercaptan in the presence of the catalyst and efiecting decomposition and condensation of the said mercaptan while evolving hydrogen sulfide and product vapors from the reaction mass, condensing the product vapors and recovering stilbene from the condensate.

5. A process of making stilbene comprising the steps of heating benzyl mercaptan at an initial refluxing temperature between about 150 C. and 325 C. in the presence of a sulfide of a metal selected from the group consisting of iron, cobalt, nickel, copper, silver, lead, manganese and molybdenum, refluxing the said mercaptan in the presence of the catalyst and efiecting decomposition and condensation of the said mercaptan while evolving hydrogen sulfide and product vapors from the reaction mass, passing an inert gas through the said refluxing benzyl mercaptan, cooling the product vapors and condensing stilbene therefrom.

6. The process of claim 5 in which the inert gas is ammonia.

7. The process of claim 5 in which the inert gas is nitrogen.

8. A process of making stilbene comprising the steps of heating benzyl mercaptan to a boiling temperature between about 150 and 325 C., bringing at least the vapors of the boiling mercaptan into contact with between 0.5 and 15 percent by weight, based on the mercaptan, of a sulfactive catalyst comprising essentially a sulfide of a metal selected from the group consisting of iron, cobalt, nickel, copper, silver, lead, manganese and molybdenum, eifecting a decomposition and condensation of the heated mercaptan while evolving hydrogen sulfide and product vapors therefrom, condensing the said product vapors, and recovering stilbene from the condensate.

LEONARD A. MA'IIANO.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 5 2,419,198 Bowman Apr. 22, 1947 FOREIGN PATENTS Number Country Date 480,756 Great Britain Feb. 28, 1938 10 OTHER REFERENCES Berkman et al., Catalysis, p. 928 (1940) pub. by Reinhold Pub. Corp., N. Y. 

1. A PROCESS OF MAKING STILBENE AND STILBENE DERIVATIVES COMPRISING THE STEPS OF HEATING A BENZYL MERCAPTAN, HAVING THE STRUCTURE: 